To precision drill or bore holes into steel, iron, and other hardened metals, a drill press or boring machine is required having a fixture or jig to maintain the work in a fixed position in combination with a drill press mechanism to accurately position, drive, and feed a drill bit into the work. In the past, these machines were quite bulky as the drill press portion must be capable of developing substantial amounts of torque and pressure in the bit against the work and the fixture must be capable of maintaining the work in a fixed position against these substantial forces. Also, large drive motors were usually required along with some type of lever action drill press mechanism for advancing and retracting the bit from the work in the feeding operation. Another requirement for the accurate boring of holes is a tool which can maintain a steady feed rate which is fully adjustable over a wide range of values for differing types of materials. This can be understood by realizing that the amount of energy required at the point of the drill bit is determined by the size of hole being bored and the shaving cut per revolution as the bit rotates and cuts into the work. If the hole is smaller or the shaving thinner, then a smaller amount of energy is required which means that a smaller amount of torque, feed pressure, and horsepower to drive the bit are needed for the boring operation. As the hole size increases or the shaving thickness is increased, then greater amounts of energy are required to step up these force requirements to accomplish the same boring operation. To provide for a smooth and even boring operation, and to minimize the heating of the drill bit a constant feed rate throughout is the most desirable operating mode. Furthermore, the drill bit may have a tendency to hang up or jam if the feed rate is suddenly decreased as the bit is boring into the work. This may result in a broken drill bit, a burned out drive motor, or if a hand drill is used, then the kick back experienced at the drill may be enough to break a man's arm. Thus, the drill press must be capable of maintaining a constant feed rate throughout a drilling or boring operation.
In the prior art, machines are available which are floor standing and are quite expensive in that lever action or gearing is used to develop the feed pressure and complicated feed mechanisms are used to ensure accurate positioning and feeding of the bit in relation to the jig or fixture. Also, the jig or fixture may be quite bulky and complicated in order to maintain the work in a fixed position while it is being bored under substantial pressure and to provide for accurate repositioning of the work during a multiple boring operation.
Applicant has developed a boring tool which is highly compact and portable and which provides many of the same advantages found in much larger and more complex drill presses and boring tools. Applicant's device has structure for accurate positioning of a work piece and has an attachment which provides for surface boring operation. Some of the features of applicant's device include a very accurate feed mechanism which is capable of developing very high torque, full bearing support between the feed means and the drilling means, an attachment which provides for an external drive means, fully interchangeable drill bits and chucks, a locking pin arrangement to provide power backing out of the drill bit away from the work, and other features as are apparent from the following description.
Applicant's boring tool may weigh as little as 35 lbs. and have a small bulk which permits use in a portable mode in very tight, cramped quarters. Conversely, applicant's boring tool may be used in a machine shop operation to replace much larger and more expensive machines otherwise required to precision drill perfect 90.degree. holes in hardened steel and other materials resistant to machining operations. A normal half inch or three quarter inch hand drill may be used to drive the drill bit in applicant's boring device as both radial and thrust bearings are provided between the drill bit and the feed means. These bearings effectively isolate the hand drill or other drive means from the drill bit and provide for a smooth and continuous drilling operation. Kick back, chattering and other difficulties sometimes experienced in other boring tools are eliminated by isolating the drill bit from the driving means.
Another advantage of applicant's device is that it is significantly reduced in bulk and size and is adapted to be used in a portable manner and for surface boring. A support plate attaches to the base plate of the device and the boring tool may be bolted to the surface being drilled by either an existing hole or a hole previously drilled by applicant's tool. Thus, the boring tool may be accurately positioned to drill a hole anywhere on a surface within a circle having a radius equal to the distance between the bit and the far end of the positioning slot in the support plate from an existing hole. The compact size of the boring tool allows the tool to be used in very tight and cramped quarters as is encountered in many construction jobs including the steel work for bridges and large buildings.
The above features and other advantages may be more fully understood by referring to the drawings and description of the preferred embodiment as follows.